The oscillatory profile shape as design parameter for optimizing continuous oscillatory baffled reactors

Continuous oscillatory baffled reactors (COBRs) are widely used to achieve plug-flow even at low flow rates. Traditionally, an oscillatory motion with a sinusoidal profile has been applied to create this plug-flow. This work investigates the potential of using the shape of the oscillatory profile as a design parameter to enhance plug-flow behavior. The profiles studied are asymmetric deviations from the commonly used symmetrical waves, meaning that the forward or backward motion occurs faster than the opposite stroke. It is demonstrated that profiles with a greater imbalance between the forward and backward strokes result in improved plug-flow behavior. Particle image velocimetry reveals that these asymmetric profiles excite additional superharmonic oscillations on top of the main excitation frequency. These additional oscillations most likely introduce more radial mixing events, resulting in the observed improvement in plug-flow behavior. Wavelet analysis shows that these superharmonics are only briefly present after the rapid forward or backward movement and disappear during the slower opposite stroke. Furthermore, the analysis reveals a positive correlation between the plug-flow behavior and the relative magnitude of these superharmonics compared to the excitation frequency. Therefore, it can be concluded that the shape of the oscillatory profile significantly influences COBR performance. This finding provides researchers with a deeper understanding of COBRs and offers engineers greater flexibility in designing COBRs for industrial applications.